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Anchiornis
Anchiornis is an extinct genus of small, feathered, maniraptoran dinosaur. The genus Anchiornis contains the type species Anchiornis huxleyi, named in honor of Thomas Henry Huxley, an early proponent of biological evolution, and the first to propose a close evolutionary relationship between birds and dinosaurs. The generic name Anchiornis means "near bird", and its describers cited it as important in filling a gap in the transition between the body plans of flying avian birds and non-avian dinosaurs.Xu, X., Zhao, Q., Norell, M., Sullivan, C., Hone, D., Erickson, G., Wang, X., Han, F. and Guo, Y. (2009). "A new feathered maniraptoran dinosaur fossil that fills a morphological gap in avian origin." Chinese Science Bulletin, six pages, accepted November 15, 2008. History of discovery The type specimen was described by paleontologist Xu Xing and colleagues in a paper accepted to the Chinese Science Bulletin in November of 2008, to be published in print in early 2009. The specimen consists of an articulated skeleton missing only the skull, part of the tail, and the right forelimb. The authors estimated that a complete individual would be 34 cm in length (13.3 in) and weigh only 110 g, making it the smallest known non-avian dinosaur. (See also Dinosaur size). The fossil was recovered from the Yaolugou locality, Jianchang County, western Liaoning, China. The deposits are lake sediment, and are of uncertain age. They may date to the Cretaceous or Jurassic periods. Description Anchiornis huxleyi was a small, paravian dinosaur with a triangular skull bearing several details in common with dromaeosaurids and troodontids. Anchiornis had very long legs, usually an indication that they were strong runners. However, the extensive leg feathers indicate that this may be a vestigial trait, as running animals tend to have reduced, not increased, hair or feathers on their legs.2 The forelimbs of Anchiornis were also very long, similar to archaeopterygids. The first fossil was recovered from the Yaolugou locality, Jianchang County, western Liaoning, China; the second, at the Daxishan locality of the same area. The deposits are lake sediment, and are of uncertain age. Radiological measurements indicate an early Late Jurassic age for them, between 161 and 151 million years ago. Feathers Paleobiology Anchiornis is notable for its proportionally long forelimbs, which measured 80% of the total length of the hind limbs. This is similar to the condition in early avians such as Archaeopteryx, and the authors pointed out that long forelimbs are necessary for flight. It is possible that Anchiornis was able to fly or glide, and may have had a functional airfoil. Anchiornis also had a more avian wrist than other non-avian theropods. Anchiornis has hind leg proportions more like those of lower theropod dinosaurs than avialans. Faint, carbonized feather impressions were preserved in patches in the type specimen. Feathers on the torso measured an average of 20 mm in length, but the feathers were too poorly preserved to ascertain details of their structure. A cladistic analysis indicated that Anchiornis was a basal member of the Avialae and the sister taxon of Aves. References Category:Dinosaurs of Asia Category:Feathered dinosaurs Category:Transitional fossil Category:Troodontids Category:Jurassic dinosaurs